This Court case essentially made the judicial branch as an important branch of the government. It did so by giving the judicial branch the power of judicial review.
The Constitution itself does not give the Court the power of judicial review. It says laws may not violate the Constitution, but it does not say who gets to say whether laws do violate the Constitution. In this case, the Supreme Court declared that the judicial branch is the one who gets to do this.
By making this claim, they set themselves up as a major power in the government. They would now be able to rule that actions of the other two branches were unconstitutional.